Double the maximum address count to accomodate IPv6

With the addition of IPv6, some computers with lots of addresses are
reaching the old address limit of 20 addresses. We'll have to see how
this works out in practise. Maybe we'll have to do the connection in
stages to prevent sending out too many packets at once (like only
connecting to the first five addresses initially, then after a timeout
the next five, and so on).

src/network/C4Network2Client.h

@@ -25,7 +25,7 @@
 class C4Network2; class C4Network2IOConnection;
 
 // maximum address count that is saved for one client
-const int32_t C4ClientMaxAddr = 20;
+const int32_t C4ClientMaxAddr = 40;
 
 // retry count and interval for connecting a client
 const int32_t C4NetClientConnectAttempts = 3,